Aspects of the present disclosure relate generally to the field of photorefractive layer stacks, electro-optical devices comprising such layer stacks, and methods of operation thereof.
A photorefractive layer stack typically comprises stacked layers of semiconductor materials designed to enable a photorefractive response (e.g., a modulation of the refractive index of the stack occurs in response to illuminating the stack with an optical pattern of modulated intensity). For example, in a bulk photorefractive material, refractive index gratings can be generated by illuminating the material by two coherent plane light waves under different angles. Due to interference, a periodic pattern of bright and dark stripes can be formed in the material. In the bright areas, light is absorbed and excites charge carriers. The (most) mobile carriers (electrons) diffuse to the dark areas where they are trapped. Thus, in the dark areas an excess negative charge builds up, while in the bright areas an excess positive charge remains. The electric-field pattern that results from this non-uniform charge distribution causes, in turn, a modulation of refractive index, owing to the electro-optic Pockels effect.